1. Field of the Invention
The present invention relates to an improved technology of an SR motor (switched reluctance motor).
2. Description of the Related Art
The SR motor has been known as the motor of the type that does not employ the magnet. Such SR motor is constructed by arranging a stator in which a plurality of inwardly projecting salient poles are formed integrally with a cylindrical yoke and a rotor which has a plurality of outwardly projecting salient poles on the same shaft and then fitting winding coils on the salient poles of the stator.
The numbers of the salient poles of the rotor and the salient poles of the stator are set to the even number respectively not to constitute the multiple relationship mutually. For example, the number of the salient poles of the rotor is four while the number of the salient poles of the stator is six, the number of the salient poles of the rotor is six while the number of the salient poles of the stator is eight, the number of the salient poles of the rotor is eight while the number of the salient poles of the stator is twelve, and so forth.
When the current is supplied to a pair of opposing winding coils (plural pairs of winding coils as the case may be) of the stator, the magnetic fluxes directed from the salient poles of the stator to the salient poles of the rotor are generated to attract the salient poles of the rotor to the salient poles of the stator, so that a torque is generated. At this time, when one salient pole of the rotor is positioned so as to face to one salient pole of the stator, positions of remaining salient poles of the rotor are displaced mutually with remaining salient poles of the stator. Therefore, if the current is supplied to the winding coils by selecting the displaced salient poles of the stator sequentially, the salient poles of the rotor are attracted successively to them. Thus, the rotor can be rotated around the shaft.
Also, such SR motor can be functioned as the generator. FIGS. 1A and 1B are circuit diagrams showing a driving circuit in the prior art when the SR motor is used as the generator-motor. This driving circuit is provided to a plurality of windings constituting the same phase (winding sets) of the winding coils, that are fitted on the salient poles of the stator, respectively. For example, in the case of the three-phase motor in which the number of the salient poles of the stator is six and the number of the salient poles of the rotor is four, each phase (U phase, V phase, W phase) is composed of a pair of mutually opposing winding coils. These pairs of winding coils are connected in series to constitute the winding sets respectively, and then the driving circuit is provided to these winding sets respectively. In this disclosure, assume that the winding coil or the winding signifies not only a single winding coil but also a plurality of winding coils constituting the same phase (winding set).
As shown in FIGS. 1A and 1B, a start terminal T1 of a winding coil C is connected to a power supply E via a power device such as a switching device (power transistor) SW1 and also connected to ground via the diode D1. An end terminal T2 of the winding coil C is connected to the power supply E via a diode D2 and also connected to ground via the power device such as a switching device SW2.
FIGS. 2A to 2C are views showing control contents of operations of the switching devices SW1 and SW2, wherein FIG. 2A shows a relationship between a rotation angle of a rotor (abscissa) and an inductance L (ordinate), FIG. 2B shows a relationship between the rotation angle of the rotor (abscissa) and a winding voltage (ordinate), and FIG. 2C shows a relationship between the rotation angle of the rotor (abscissa) and a winding current (ordinate).
When the rotation angle of the rotor becomes a predetermined angle (xcex8on) during a period in which the inductance L is decreasing, the voltage is applied to the winding coil C by turning ON the switching devices SW1 and SW2 simultaneously. At this time, as shown in FIG. 1A, a current flows through a route consisting of the switching device SW1, the winding coil C, and the switching device SW2 and thus energy is supplied from the power supply E to generate the torque.
Then, when the rotation angle of the rotor becomes another predetermined angle (xcex8off) during the period in which the inductance L is still decreasing, the switching devices SW1 and SW2 are turned OFF simultaneously. At this time, as shown in FIG. 1B, a current flows through a route consisting of the diode D1, the winding coil C, the diode D2 due to an electromotive force caused in the winding coil C to return the energy to the power supply E. Regenerative energy can be increased larger than supply energy by controlling the operations of the switching devices SW1 and SW2 in this manner, whereby the SR motor can be operated as the generator.
However, according to the controlling method in the prior art, the large current is caused to flow because the electromotive force is small, particularly in the low rotational range. As a result, there is such a problem that, since the power device having a large current capacity must be employed as the power device containing the switching device, cost is increased and the size of the device becomes large. Also, there is such another problem that copper loss of the winding is increased and thus the operation of the SR motor becomes ineffective. In addition, there is such still another problem that torque ripple and flutter is also increased correspondingly, since current extremely increases.
The present invention has been made in light of the above problems in the prior art, and it is an object of the present invention to provide an SR motor controlling method and an SR motor, which are capable of achieving highly effectively the reduction in cost and the improvement in performance.
In order to solve the above problems, according to an aspect of the present invention, there is provided a method of controlling an SR motor which includes a stator having a plurality of salient poles, windings wound around the plurality of salient poles and generating magnetic fields in the plurality of salient poles, and a rotor having another plurality of salient poles, a number of the salient poles of the rotor being determined depending upon a number of the salient poles of the stator, the method comprising: executing, changeably as the rotor rotates, a supply mode for supplying power from a power supply to the windings, a reflux mode for setting both terminals of the windings to an identical potential, and a regenerative mode for recovering an electromotive force generated in the windings into the power supply.
In a preferred embodiment of the present invention, the supply mode, the reflux mode and the regenerative mode are executed in that order.
In a preferred embodiment of the present invention, after the supply mode is executed, a repetitive mode during which the regenerative mode and the reflux mode are repeated alternatively is executed.
In a preferred embodiment of the present invention, after a first supply mode is executed, a first repetitive mode during which the regenerative mode and a second supply mode are repeated alternatively and a second repetitive mode during which the regenerative mode and the reflux mode are repeated alternatively are mixedly executed.
In order to solve the above problems, according to another aspect of the present invention, there is provided a method of controlling an SR motor which includes a stator having a plurality of salient poles, windings wound around the plurality of salient poles and generating magnetic fields in the plurality of salient poles, and a rotor having another plurality of salient poles a number of the salient poles of the rotor being determined depending upon a number of the salient poles of the stator, the method comprising: executing a first supply mode for supplying power from a power supply to the windings; and then executing a repetitive mode during which the regenerative mode for recovering an electromotive force generated in the windings into the power supply and a second supply mode for supplying the power from the power supply to the windings are repeated alternatively.
In order to solve the above problems, according to still another aspect of the present invention, there is provide an SR motor which includes a stator having a plurality of salient poles, windings wound around the plurality of salient poles and generating magnetic fields in the plurality of salient poles, and a rotor having another plurality of salient poles, a number of the salient poles of the rotor being determined depending upon a number of the salient poles of the stator, the SR motor comprising: a first switch configured to connect selectively start terminals of the windings to one polarity of a power supply; a second switch configured to connect selectively end terminals of the windings to other polarity of the power supply; a first diode interposed between the start terminals of the windings and the other polarity of the power supply, and configured to flow a current only in a direction toward the start terminals; a second diode interposed between the end terminals of the windings and one polarity of the power supply, and configured to flow the current only in a direction toward one polarity of the power supply; and a controller configured to control to execute, changeably as the rotor rotates, a supply mode in which the first switch and the second switch are connected simultaneously, a reflux mode in which one of the first switch and the second switch is connected and other of them is cut off, and a regenerative mode in which the first switch and the second switch are cut off simultaneously.
In a preferred embodiment of the present invention, the supply mode, the reflux mode and the regenerative mode are executed in that order.
In a preferred embodiment of the present invention, after the supply mode is executed, a repetitive mode during which the regenerative mode and the reflux mode are repeated alternatively is executed.
In a preferred embodiment of the present invention, after a first supply mode is executed, a first repetitive mode during which the regenerative mode and a second supply mode are repeated alternatively and a second repetitive mode during which the regenerative mode and the reflux mode are repeated alternatively are mixedly executed.
In order to solve the above problems, according to yet another aspect of the present invention, there is provide an SR motor which includes a stator having a plurality of salient poles, windings wound around the plurality of salient poles and generating magnetic fields in the plurality of salient poles, and a rotor having another plurality of salient poles, a number of the salient poles of the rotor being determined depending upon a number of the salient poles of the stator, the SR motor comprising: a first switch configured to connect selectively start terminals of the windings to one polarity of a power supply; a second switch configured to connect selectively end terminals of the windings to other polarity of the power supply; a first diode interposed between the start terminals of the windings and the other polarity of the power supply, and configured to flow a current only in a direction toward the start terminals; a second diode interposed between the end terminals of the windings and one polarity of the power supply, and configured to flow the current only in a direction toward one polarity of the power supply; and a controller configured to control to execute a first supply mode in which the first switch and the second switch are connected simultaneously, and then execute a repetitive mode in which the first switch and the second switch are cut off simultaneously and a second supply mode in which the first switch and the second switch are connected simultaneously.
The nature, principle and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.